The present invention concerns novel diazo derivatives of general formula (I) hereafter reported, the process for their preparation and their use as deacidifying agents in the deacidification treatment of paper.
It is universally acknowledged that one of the causes of the too rapid deterioration of cultural materials on paper is the presence of acidity in the material. p In modern paper, acidity is usually caused during the manufacture in the paper factory; however, acidity can often be found even in papers or books that are made from acid-free paper, as it comes from some types of ink for manuscripts, that was widely used in the past.
Experts agree that in order to prolong the life of books and documents that are stored in libraries and archives (according to the experts from three to five times as much) it is necessary to eliminate the acidity from the materials, by using a technique that in the specialised environment is known as xe2x80x9cdeacidificationxe2x80x9d. Obviously, in order to avoid the errors committed in the past, new documents and books to be stored should be made with acid-free paper (UNI n. 10332xe2x80x94Paper for documents. Requirements for the maximum duration and durability and UNI n. 10333xe2x80x94Paper for documents. Requirements for duration).
In the Italian public libraries there are currently 30 million books; an equal amount of paper documents are kept in public archives.
From fragmentary surveys carried out in some Italian preservation environments, in agreement with similar research carried out abroad on a wider scale, it has been found that 20-30% of library and archive materials are now so fragile that they cannot be made available for free consultation; the risk of further damage would be too high. Alongside this relatively low percentage however, it has been found that 60-80% of preserved books and documents need to be deacidified or in some way stabilised; otherwise, it would only be a matter of time before all the acid material would become fragile, and no longer consultable.
In view of what above said, it is evident that, in order to protect the Italian book and document heritage, it is necessary to be able to intervene with mass deacidification techniques, or however, with stabilisation techniques that would slow down deterioration; these would be techniques that allow the entire heritage to be restored in a time span of no more than ten, fifteen years.
It is therefore much felt the need for products that allow effective and persistent deacidification of paper, without secondary effects on the material treated.
The Applicant has now found novel diazo derivatives of general formula (I) that are effective as deacidifying agents in the deacidification treatment of paper, without showing the drawbacks of the deacidification methods that have been used so far, and a process for their preparation.
Therefore subject of the present invention are the diazo derivatives of general formula (I) 
wherein Rxe2x80x2 is chosen from H and methyl, and R is the group 
where n=1, 2, 3, 4, 5; and R1 and R2, equal to one another, are chosen between methyl and ethyl, or R1 and R2, taken together, form with N a piperidine ring or a 4-morpholine ring;
provided that, when n=2 and Rxe2x80x2=H, R1 and R2 are different from methyl.
Further subject of the invention is the process for the preparation of the diazo derivatives of general formula (I) 
wherein Rxe2x80x2 is chosen from H and methyl, and R is the group 
where n=1, 2, 3, 4, 5; and R1 and R2, equal to one another, are chosen between methyl and ethyl, or R1 and R2, taken together, form with N a piperidine ring or a 4-morpholine ring;
comprising the following steps:
a) reaction between the amine of formula (II) and ethyl chlorocarbonate of formula (III) to obtain carbamate (IV) 
xe2x80x83in which R is defined as above;
b) nitrosation of the carbamate (IV) obtained from the step a) to obtain N-nitroso-carbamate of formula (V): 
xe2x80x83wherein R is defined as above;
c) reduction of the N-nitroso-carbamate (V) obtained from step b) to obtain the desired formula (I) compound: 
xe2x80x83wherein R and Rxe2x80x2 are defined as above.
Further subjects of this invention are the formula (IV) compounds and their N-nitroso derivatives of formula (V); and the use of the formula (I) compounds in the deacidification methods of paper material.
According to a particular embodiment of the present invention, step a) of the present process is carried out at room temperature using CH2Cl2 as a solvent, and with a large excess of K2CO3 so as to completely neutralise the HCl that forms during the,reaction; the preferred stoichiometric ratio between amine (II), K2CO3 and ethyl chlorocarbonate (III) is 1:4:3.
The reaction in step b) of the present process can be carried out at a temperature of 1-2xc2x0 C. using HCl/NaNO2 as reagent. A large excess of HCl/NaNO2 is preferably used so as to achieve complete nitrosation of the formula (IV) product.
According to a particular embodiment of the invention, step c) of the present process is carried out at a temperature of 1-2xc2x0 C. with a solution of sodium methoxide in methanol. By using a slight excess of sodium methoxide compared to the amount of the formula (V) compound, the formula (I) compound is obtained in which Rxe2x80x2 is H, whereas with a large excess of sodium methoxide, the compound (I) is obtained in which Rxe2x80x2 is methyl. Methanol, ethanol and Na2CO3are obtained as the only secondary reaction products.
The so obtained product is dissolved in a suitable inert stabilising solvent, preferably in diethyl ether, and the ether solution of the products is kept at a temperature of xe2x88x9218xc2x0 C. and away from light, and it is used in this form without isolating the product.
The formula (I) compounds can be used for the deacidification of paper products according to techniques known in the art; preferably, these compounds can be used in mass deacidification techniques, where xe2x80x9cmass deacidification techniquesxe2x80x9d means the technique described in the copending patent application in the name of the same Applicant, wherein an increase in the pH up to 9-10 of the paper material treated is obtained, and such an increase persists in time for at least 6 months. Following the treatment with compounds of general formula (I) prepared with the present process, no undesired side effects were noted, such as the formation of unpleasant odours or colouring caused by the treatment itself.
The present compound of formula (I) wherein Rxe2x80x2 is H and R is the group 
where n=1, and R1 and R2, taken together, from with N a piperidine ring, has proved to be especially effective in obtaining a prolonged continuation of the basic pH obtained by the deacidification treatment.
The following examples are given to provide non-limiting illustrations of the present invention.